1. Field of the Invention
The invention relates to a process of sulfonation of poly(ether sulfones) that is known to be notoriously difficult to sulfonate. The novel sulfonated poly(ether sulfones) and derivatives thereof are useful as membrane forming materials for a variety of separation processes, e.g. reverse osmosis, ultra-filtration, ion exchange and like processes.
2. Brief Description of the Prior Art
Sulfonation of polysulfones is disclosed in U.S. Pat. No. 3,709,841, wherein Quentin describes a preparation of polymers in which part of the aromatic rings are substituted with hydroxysulfonyl radical (.about.SO.sub.3 H, also called sulfonic groups). However, aromatic poly(ether sulfones) made up of repeating units of the formula: ##STR1## are notoriously difficult to sulfonate due to the electron withdrawing effect of the sulfone linkages which deactivate the adjacent aromatic rings for electrophilic substitution. Sulfonation of these polymers with chlorosulfonic acid or oleum at ambient temperatures require an enormous excess of sulfonation agent and results in a highly degraded product with extents of sulfonation that are impossible to control. The surplus of sulfonation agents complicate the workup procedures (see U.S. Pat. No. 4,273,903, Examples 10, 11 and 12). In order to overcome the above difficulties, copolymers of the above polysulfones were prepared that contained in addition to the repeat unit (I) described above, a variable amount of easily sulfonatable units of the formula: ##STR2## (see the above cited U.S. Pat. No. 4,273,903).
It was found in the present invention that aromatic poly(ether sulfones) can be sulfonated to controlled degrees of substitution with sulfonating agents. The degree of substitution is controlled by the choice of and mole ratio of sulfonating agent to aromatic rings of the polymer, by the reaction temperature and by the time of the reaction.
Customarily, sulfonation of poly(ether sulfone) polymer is carried out homogeneously, i.e.; by putting the polymer into solution before the addition of a sulfonating agent. This invention concerns a method for carrying out sulfonation in a heterogeneous manner, i.e.; sulfonation of the precipitated polymer crystals.